JP4774883B2 - Zinc-based alloy shot - Google Patents

Description

  The present invention relates to a novel zinc-based alloy shot made of a zinc-based alloy. In particular, the invention relates to a zinc-based alloy shot suitable for surface finishing of light alloy castings (castings) such as aluminum castings.

  Here, the casting includes not only a casting that uses the gravity of the molten metal, but also die casting that applies pressure to the molten metal, centrifugal casting that pours the molten metal into the mold by centrifugal force while rotating the mold, etc. Includes special castings.

  In the present specification and claims, the concentration unit “%” means “mass percentage” as usual.

  Aluminum castings are usually subjected to surface treatment after mold release by colliding metal spheres (shots) on the surface with air pressure or the rotational force of impeller blades. This is to remove burrs and burrs generated in the casting after mold release and to remove scale (casting sand).

However, with a normal steel ball shot, the hardness is too high, and the surface to be treated may be worn or deformed. For this reason, a zinc-based alloy shot that is a soft metal and has almost no risk of dust explosion is used. Zinc has an explosion sensitivity of 0.6, which is very low compared to 7.5 of aluminum. (See Patent Document 1, paragraph 0003)
However, the zinc-based alloy shot tends to be in a grayish dark state as a whole because the color of the material in the article to be processed, such as an aluminum casting, is lost, and the commercial value is impaired.

  Therefore, Patent Document 1 proposes a technique for forming a shot with a zinc-based alloy in which 0.05 to 2.0% (desirably, 0.10 to 1.0%) of Cu is contained in zinc.

  On the other hand, the appearance of shots with high hardness (high hardness) has been demanded in order to improve productivity, that is, to shorten blast time and extend shot life.

  Therefore, in order to increase the hardness of the shot, a technique for forming a zinc-based alloy shot having a Vickers hardness of 60 to 130 HV by containing 0.3 to 5.0 mass% of Mn in zinc is disclosed in Patent Document 2. Has been proposed.

  Note that Patent Document 3 exists as a related reference for increasing the hardness of a zinc-based alloy shot.

However, due to the recent demand for surface design, it is required that no blackening occurs (no discoloration). Furthermore, due to the demand for productivity, even if the hardness is increased, the product after blasting must be fine. There has been a demand for a material that does not cause overall wear and hardly causes surface roughness.
Japanese Patent No. 2887228 JP 2001-162538 A JP-A-11-320416

  In view of the above, it is an object of the present invention to provide a zinc-based alloy shot that can satisfy the above-mentioned demand.

  As a result of intensive studies to solve these problems, the present inventors have found that the above problem can be solved if copper (Cu) and manganese (Mn) are used in combination and Cu is added in a larger amount than Mn. Thus, the present invention having the following configuration has been conceived.

  In a shot made of a zinc-based alloy, the zinc-based alloy is such that copper (Cu) and manganese (Mn) as solute metals have a Cu / Mn mass ratio> 1, and Vickers hardness (JIS Z 2244). It is added so that it may show 55-180HV.

  When copper and manganese are added in the relationship of the former> the latter, as shown in the examples described later, a shot with a larger hardness than that obtained when each of the total addition amount of copper and manganese (Cu + Mn) is added alone is obtained, and As a result, almost no discoloration (darkening) occurs in the article to be processed by blasting (Example 2 and Comparative Example 3 described later, Example 3 group and Comparative Example 4). Naturally, it is difficult to obtain the hardness of the present invention by adding only copper or manganese, and if they are excessively blended, they become brittle (see Patent Document 1, paragraph 0009, Patent Document 2, paragraph 0015). That is, in order to obtain a shot with a high hardness using copper or manganese, it is necessary to add a large amount of copper or manganese, and the toughness of zinc is lowered, so that the shot life is reduced (easy to wear). On the other hand, when a shot having the same hardness as the conventional one has a relationship of copper> manganese of the present invention, a small amount of copper and manganese can be added, and a shot with high toughness can be obtained (shot wear is reduced). This contributes to the longer shot life.)

  The Cu / Mn (mass) ratio is set to Cu / Mn ratio≈1.5 to 6, preferably 2 to 3. The Cu / Mn ratio is not absolute, and defines a range that can be inferred from test examples and empirical rules conducted by the present inventors, and “≈” includes the meaning.

  If the copper ratio is too high, it is necessary to increase the absolute addition amount of manganese in order to increase the hardness. Conversely, if the copper ratio is too low, it is necessary to increase the absolute addition amount of copper in order to eliminate darkening. There is. Therefore, the total absolute amount of both solute alloy elements increases, making it difficult to obtain a shot with relatively stable quality (hardness, etc.). (See Patent Document 2, paragraph 0010, lines 12-13).

  In the above configuration, the copper and manganese are preferably added so as to have a Vickers hardness of about 60 to 160 HV. This hardness range shows a more desirable range when blasting general-purpose aluminum die castings, etc., depending on the hardness and required finish of the product to be processed, and the type of zinc (hardness) that is the base material <matrix> ), Etc., and not absolute. The meaning is included in “about”.

  When the Vickers hardness of the shot (zinc-based alloy) is less than about 60 HV, it takes time to deburr and scale off, and it is difficult to shorten the blast time which is one of the objects of the present invention. On the other hand, when a large amount of copper and manganese is added in order to obtain a product of about 160 HV or more, the material becomes brittle (no toughness), and on the contrary, the shot life is shortened (see Examples 4 and 5).

  The particle diameter of the shot is not particularly limited as long as it can be shot, but is preferably about 0.05 to 5 mm, and more preferably about 0.3 to 4 mm. This range also varies depending on the hardness and blasting conditions of one or both of the shot and the product to be processed, and is derived from test examples and empirical rules conducted by the present inventors, and is not absolute. The “about” in front of the numerical value includes its meaning.

  If the shot particle size is too small, even with the same hardness, blasting time is increased and burrs are easily left behind (see Example 3-1). On the other hand, if the shot particle size is too large, fine wear and overall wear / deformation are likely to occur on the surface of the article to be processed even with similar hardness (see Example 3-6).

The amount of each solute metal added is usually about 0.8 to 6% (preferably about 1.5 to 4.0%) for copper and about 0.2 to 5% (preferably about 1) for manganese. 0.0 to 3.0%) and the total amount of copper and manganese is about 1.0 to 10.0%. The addition amount of copper and manganese and the total amount thereof are not absolute, as described above, and differ depending on the type of zinc (grade) of the base metal and the grade of copper and manganese. The meaning is included in “about” before the numerical value. Furthermore, when adding a small amount of solute metals other than copper and manganese (for example, Fe, Ni, etc.), it fluctuates. In the composition of the present zinc-based alloy, the balance of elements other than copper (Cu) and manganese (Mn) is naturally composed of zinc (Zn) and inevitable impurities (substantially composed only of Zn).

  If the amount of copper added is too small, it is difficult to reliably eliminate blackening. On the other hand, if the amount of manganese added is too small, improvement in hardness cannot be expected, and one or both of copper and manganese, or the total amount added. If the amount is excessive, shot toughness decreases, shot wear increases, and the shot life is shortened.

  In addition, it does not specifically limit as zinc, copper, and manganese used by the shot of this invention, It can select and use suitably from what is marketed.

  In addition, zinc as a base material is usually commercially available with a Vickers hardness in the range of 40 to 50 HV, and a relatively low hardness is easy to obtain toughness. , Deburring and other cleaning workability is reduced. In the test example of the present invention, even if the addition amount of copper or manganese is the same, the shot hardness is relatively low because in this test example, a grade with low hardness is used as the base material zinc. In addition, as shown in Patent Document 1, a small amount of iron is added together with copper.

  The shot can be manufactured by a conventional method. In the following, from paragraph 0008 of Patent Document 1, paragraph 0009 of Patent Document 2, and the like, the expression is appropriately changed according to the present invention.

  “A mixture obtained by adding copper and manganese in zinc in a predetermined ratio and in a predetermined ratio is heated and melted (molten metal temperature: 450 to 650 ° C.) in a reducing atmosphere to form a molten metal. To obtain a spherical granular material solidified and deposited in this cooling medium, which is recovered, dried, classified and selected by sieving, etc. Divide into shots. "

  A mixture of each zinc-based alloy composition shown in Table 1 is heated in an inert atmosphere having a nozzle having a predetermined diameter at the bottom to prepare a molten metal (molten metal temperature of 600 to 620 ° C.). The molten metal is put in a graphite crucible having a flow hole with a predetermined diameter at the bottom, pressurized from the upper surface of the molten metal and allowed to flow into water, and the resulting agglomerated spheroids are collected, dried and classified to display the indicated particle size and Vickers. The shot of each Example and Comparative Example of hardness was obtained.

  Using each shot obtained in this way, an aluminum wheel (die-cast product) (outer diameter: 43.2 mm, average wall thickness 10 mm) was used as a workpiece, and blasting (deburring with 5 HP) was performed using a blasting device (5HP centrifugal projection type). Scale down).

  The processing conditions at that time were shot projection speed: 45 m / s and shot projection amount: 50 kg.

  And the following each item was evaluated.

1) Deburring:
It was judged whether or not “burrs” were removed by visual inspection, and a four-step evaluation was performed based on the completion time of deburring.

Within 30 seconds: ◎, over 30 seconds within 60 seconds: 〇, over 60 seconds within 90 seconds: △
90 seconds or more: ×
2) Color after processing:
The color tone on the processed surface of the work piece was visually judged and evaluated in four stages according to the following criteria. In addition, the surface of the workpiece before blasting is in a state where the color tone is silver white and the casting scale is attached.

The whole surface is silver white: ◎, some silver white: 〇, some darkening: △
Fully blackened: ×
3) Surface condition:
In order to comprehensively judge the polishing situation on the surface of the work piece after processing, "scale removal", "rough surface", "abrasion of fine features" and "whole wear / deformation" are evaluated items. The following four grades were evaluated.

Descaling (OK), surface roughness (none), wear of fine features (none), overall wear and deformation (none) ... ◎
Scale removal (OK), rough surface (slightly present), fine shape wear (none), overall wear / deformation (none) ··· Scale removal (OK), rough surface (present), fine shape Part wear (somewhat present), overall wear / deformation (none) ・ ・ ・ △
Scale removal (OK), surface roughness (existence), wear of fine shaped parts (existence), overall wear / deformation (exist slightly) ... ×
4) Shot wear:
The shot projection time was set to 8 h, the amount of the shot worn and refined was measured, and four-stage evaluation was performed according to the following criteria.

0.08 kg / (h · HP) or less: ◎,
0.08 kg / (h · HP) over 0.09 kg / (h · HP) or less: Yes
0.09 kg / (h · HP) over 0.12 kg / (h · HP) or less: Δ
More than 0.12 kg / (h · HP): ×
5) Overall evaluation:
Each evaluation item of said 1-4 was comprehensively judged and it was set as 4 step | paragraph evaluation.

Extremely good: ◎, good: ◯, slightly bad: △, bad: ×
From Table 2 showing the results, the following can be understood.

  1) When copper or manganese is used alone (Comparative Examples 1 and 2), those having a high copper ratio have the same total copper / manganese addition amount (Example 2: Cu / Mn = 4.0, Cu + Mn = 2.5%) Of course, even if the total amount added is small (Example 1: Cu + Mn = 1.5%), shots with higher hardness can be obtained, excellent deburring properties, and almost no change in color tone. .

  When the manganese ratio is high (Comparative Example 4: Cu / Mn = 0.67), the total addition amount is the same as in the above case, and the copper ratio is high (Example 2: Cu / Mn = 4). 0.0), it is difficult to obtain a material with high hardness, and it is understood that darkening is likely to occur on the surface after processing. Moreover, even if the copper ratio is high, if the amount of manganese added is too small (Comparative Example 3: Cu / Mn = 10.0, Mn = 0.1%), it is difficult to obtain a shot with practical hardness, and the required burrs. It is difficult to obtain a good color tone.

  And even when the shot hardness is the same (110 HV) with the same composition, when the particle size is in the appropriate range (0.3 to 4.0 mm) as in the past (Examples 3-2 to 3-5), Although it is not ◎ in the surface condition (◯), all other items are ◎.

  When the shot particle size is too small (Example 3-1), it may be possible to use depending on the workpiece, although a slight problem occurs in deburring properties. Conversely, when the shot particle size is excessive (Example 3-6), the surface condition after processing is not good and the shot life is slightly short, but the blasting conditions (projection speed, etc.) are changed and the type of workpiece (Hardness) is considered to be practically usable.

  Further, when the total amount of added copper and manganese is increased and the shot hardness becomes close to 180 HV (Example 5), the shot life tends to be shortened. It is thought that it can be used practically by changing

Claims (6)

In a shot made of a zinc (Zn) based alloy, the zinc based alloy contains copper (Cu) and manganese (Mn) as solute metals, Cu = 0.8-6%, Mn = 0.2-5 %, Cu + Mn = 1.0 to 10.0%, and a Cu / Mn mass ratio> 1 is satisfied, and Zn = remainder, Vickers hardness (JIS Z 2244; the same applies hereinafter) 55 zinc-based alloy shot, characterized in that shows the ～180HV. Cu = 1.5 to 4.0%, zinc-based alloy shot according to claim 1, characterized in that a Mn = 1.0 to 3.0%. Zinc-based alloy shot of claim 1 or 2, wherein the said a Cu / Mn weight ratio = 1.5-6. Zinc-based alloy shot of claim 3 wherein the Cu / Mn weight ratio = 2 to 3. Zinc-based alloy shot according to any of claims 1 to 4, characterized in that indicating the Vickers hardness 60 ~160HV. The zinc-based alloy shot according to any one of claims 1 to 5 , wherein a particle diameter is 0.05 to 5.0 mm.